In recent years, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-in HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to each other because high output and large capacity are necessary for the middle or large-sized devices.
Preferably, a middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit battery) of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is easy to modify the shape of the pouch-shaped battery.
Meanwhile, Deutsches Institut fur Normung (DIN) of lithium secondary battery cells standardized by Verband der Automobilindustrie Deutschland (VDA) adopts prismatic battery cells having a rectangular parallelepiped shape. The number of cases in which standardized prismatic battery cells are applied to products has increased all over the world.
For pouch-shaped batteries, each of which uses an aluminum laminate sheet as a sheathing member unlike can type battery cells, however, it is difficult to retain a rigid rectangular parallelepiped shape corresponding to a standard size. For this reason, it is necessary to further provide a rigid part for surrounding the outside of each pouch-shaped battery.
FIG. 1 is a perspective view typically showing a conventional representative battery cell.
Referring to FIG. 1, a battery cell 10 is a plate-shaped battery cell 10 having electrode tabs 11 and 12 formed at one side thereof. Specifically, the plate-shaped battery cell 10 is configured to have a structure in which an electrode assembly (not shown) is mounted in a pouch-shaped case 13 made of a laminate sheet including a metal layer (not shown) and a resin layer (not shown), which is generally referred to as a pouch-shaped battery cell 10.
In addition, the pouch-shaped case 13 is configured to have a laminate structure including a resin layer and a metal foil layer. Consequently, it is possible to bond the pouch-shaped case 13 by applying heat and pressure to a sealed portion 14 so as to fuse the resin layer. According to circumstances, the pouch-shaped case 13 may be bonded using an adhesive.
However, the mechanical strength of the sheathing member 13 is low. For this reason, battery cells (unit batteries) are mounted in a pack case, such as a cartridge, so as to manufacture a battery module having a stable structure. On the other hand, a device or a vehicle, in which a middle- or large-sized battery module is installed, has a limited installation space. Consequently, in a case in which the size of the battery module is increased due to the use of the pack case, such as the cartridge, the spatial utilization is lowered. In addition, the battery cell repeatedly expands and contracts during charge and discharge of the battery cell due to low mechanical strength of the battery cell with the result that thermally bonded regions may be serrated from each other.
Therefore, there is a high necessity for a battery module that is capable of solving the problem of the pouch-shaped battery cell in that the mechanical strength of the pouch-shaped battery cell is low and achieving a standard-sized prismatic battery cell structure having a rigid rectangular parallelepiped shape.
Meanwhile, battery cells constituting such a middle or large-sized battery module may be secondary batteries which can be charged and discharged. Consequently, a larger amount of heat is generated from such high-output, large-capacity secondary batteries during charge and discharge of the secondary batteries. In particular, the laminate sheet of each pouch-shaped battery widely used in the battery module has a polymer material exhibiting low thermal conductivity coated on the surface thereof with the result that it is difficult to effectively lower overall temperature of the battery cells.
If the heat, generated from the battery module during charge and discharge of the battery module, is not effectively removed from the battery module, the heat accumulates in the battery module with the result that deterioration of the battery module is accelerated. According to circumstances, the battery module may catch fire or explode. For this reason, a battery pack for vehicles, which is a high-output, large-capacity battery, needs a cooling system that is capable of cooling battery cells mounted therein.
A battery module mounted in a middle or large-sized battery pack is generally manufactured by stacking a plurality of battery cells with high integration. In this case, the battery cells are stacked in a state in which the battery cells are arranged at predetermined intervals such that heat generated from the battery cells during charge and discharge of the battery cells can be removed. For example, the battery cells may be sequentially stacked in a state in which the battery cells are arranged at predetermined intervals without using an additional member. Alternatively, in a case in which the battery cells have low mechanical strength, one or more battery cells may be mounted in a cartridge and then a plurality of cartridges may be stacked to complete a battery module. Coolant channels are defined between the stacked battery cells or between the stacked battery modules so that heat accumulated between the stacked battery cells or between the stacked battery modules can be effectively removed.
In this structure, however, it is necessary to provide a plurality of coolant channels corresponding to a plurality of battery cells with the result that the overall size of the battery module is increased.
In addition, in a case in which a plurality of battery cells is stacked, coolant channels are formed such that the width of each respective coolant channel is relatively small in consideration of the size of the battery module. As a result, design of a cooling structure is complicated. That is, high pressure loss is caused in the coolant channels, each of which has a width smaller than the width of a coolant inlet port. For this reason, it is very difficult to design the shape and position of a coolant inlet port and a coolant output port. In addition, a fan may be further installed so as to prevent such pressure loss, which leads to restrictions in design due to power consumption, noise, and an installation space of the fan.
Furthermore, cooling efficiency intended in design may not be obtained due to thermal conduction resistance present between members used to constitute the cooling structure.
Therefore, there is a high necessity for a battery module which is capable of providing more improved safety and stability than a conventional rigid can type battery cell, achieving a standard-sized prismatic battery cell structure utilizing a conventional pouch-shaped battery cell, and providing excellent cooling efficiency.